“Simple trumps complete” – a 5% feature (used by less than 5% of all users) is a distraction for all the other users, and is better removed, unless its really critical (a small number of users do need to cancel service, for example).

I have this mental model of particles of attention that a user brings, a finite quantity that they will spread around according to what catches their attention. I call them “attentrons”. An extra tab or button will attract a bunch of attentrons that are not then available to focus on other areas. So the tab had better be *better* than the competing areas of the site to avoid diluting the results, or it’s better off removed.